1. Field of the Invention
The invention relates to a projection lens for a microlithographic projection exposure apparatus, and in particular for a projection exposure apparatus designed for projection light in the short-wave UV and EUV range.
2. Description of Related Art
In microlithography projection lenses with mirrors as imaging components are used for projection light in the short-wave UV and EUV ranges. For example, EP 1 178 356 A2 discloses a projection lens for microlithography which has six coaxial mirrors. This known projection lens has a diaphragm which is arranged on the second of the six mirrors of the lens.
Because the diaphragm is combined with one of the mirrors it is possible to change the diaphragm aperture only with great difficulty. The whole mirror supporting the diaphragm must be removed and replaced by an optically equivalent mirror supporting another diaphragm. This means that the lens must be readjusted, and care must be taken to close the lens again in a vacuum-tight manner and to re-evacuate the lens.